Analysis of the Accuracy of Radar Forward Operators in Simulation of a Supercell Storm

Peter McAward

23 September 2016, 3:00 PM

It is well recognized that the storm microphysical properties are very important for successfully prediction of severe thunderstorms, but are not well understood. Radar data observations and numerical modeling are two complementary tools to solve this problem. To cross-validate both observations and numerical models with different microphysics schemes, forward operators that convert model variables into radar observations are needed. Various forward operators have been developed during past years. For example, the simple Rayleigh operator converts model variables rain, snow and hail mixing ratios into radar reflectivity (Z) using the Rayleigh approximation. A relatively more complex dual-pol simulator developed by Center for Analysis and Prediction of Storms (CAPS) links model hydrometer variables into radar dual-pol observations including Z, differential reflectivity (Zdr), correlation coefficient (ρ_hv), and specific differential phase (Kdp), by using a rigorously calculated t-matrix and allowing for Mie scattering.

The present study examines three adjustments made to the current Rayleigh radar operators to improve reflectivity calculations. The first is a change in the model used for the dielectric constant for melting ice hydrometeors, the second is incorporating the continuous melting model used in dual-pol simulators, and the third is adding in a category for dry (frozen) hail/graupel hydrometeors. These adjustments led to an overall decrease in ice-phase reflectivity values that brought the simulated Z closer to what is calculated by the more rigorous dual-pol simulator.